Home networks or PANs (Personal Area Networks) are designed to interconnect digital communications devices, for example telephones, personal digital assistants, speakers, television units and multimedia players situated in proximity to the user. The range of such a network is of the order of a few meters. The nodes of such a network may be source nodes (or sender nodes), receiver nodes, relay nodes (which relay information from a first node to a second node), said nodes possibly having one or more antennas and combinations of functions.
Home networks can be wired (USB, Ethernet, Firewire) but can also rely on the use of a wireless medium. The term used for such a network is “wireless personal area network” or WPAN. The Bluetooth standards (IEEE 802.15.1), UWB, ZigBee (IEEE 802.15.4), IEEE 802.11 or IEEE 802.15.3 are presently the ones most used for this type of network.
Most of these protocols generally use a time division multiple access (TDMA) mode.
The TDMA mode is a multiplexing mode for transmitting several signals on a single channel. This is a time multiplexing mode using the principle of sharing the available time between the different connections (set up by nodes). By this means, a same carrier frequency can be used by several nodes. Each node of a network is assigned one or more time slots for the transmission of its own data and possibly for the relaying of data coming from other nodes. Each node thus sends at predetermined points in time in the network cycle.
Such wireless home networks use varied transmission frequencies, for example of the order of 60 GHz that are particularly well-suited to transmitting data at very high bit rates over a limited range. For example, the different elements of a home cinema form a network of this kind to exchange audio and/or video data at very high bit rates (beyond one gigabit per second) over a limited range of the order of about ten meters. Such wireless systems, although advantageous from the viewpoint of their intallation, nevertheless have high sensitivity to interference and masking or shadowing phenomena. This phenomenon of shadowing takes the form of the loss of a piece of data transmitted between a sender and a receiver, following the presence of an unexpected obstacle on the transmission path, such as for example a human passing between the sender and the receiver at the time of transmission. Thus, the relevance of using data paths between the various nodes of the network is heavily correlated with the progress of the positioning of the various mobile obstacles in the coverage area of the network; these obstacles are all so many dynamic shadowing phenomena for the network.
In the face of this shadowing phenomenon, the method of multiple transmissions of data symbols sent out on the network may prove to be particularly efficient to ensure efficient reception beyond a predefined residual bit error rate. This is the role of the relay nodes. This method is particularly well suited to applications requiring little bandwidth (of the order about 10 Mbps) such as the transmission of audio data or control or command data.
Such wireless networks are generally characterized by their scalability, i.e. their capacity to perceive the number of nodes forming part of the network evolve in time. Wireless nodes that are portable (digital camcorders, portable multimedia players etc.) or non-partable (such as wireless audio speakers) are capable of linking up to the wireless network randomly. This increases the number of requests for modifying the distribution of the bandwidth sent out by the nodes of the network, this number being already great to adapt the re-transmission scheme (or redundancy scheme) of the network to the developments and progress of interference (for example masking) on the radio communications links. In both cases, it proves to be essential to consider the latency with which a request for modifying bandwidth allocation is taken into account.
There are several known techniques for managing the distribution of bandwidth in a wireless network using a TDMA mode of access to the medium.
One known technique relies on the implementation in the network of a master node for determining a scheme for distributing bandwidth and transmitting it to the other nodes of the network, at each TDMA cycle. Thus, each node of the network knows about the distribution of the time slots of access to the medium (i.e. the distribution of the bandwidth) as well as the duration and position in the TDMA cycle of the time slot allotted to each node. This technique is presented especially in the US patent document 2008/0019347. This technique has the major drawback of being costly in terms of bandwidth. Indeed, the size of the bandwidth distribution scheme transmitted by the master node is great (up to about 32 kbits). Furthermore, owing to the particularly random nature of this type of wireless transmission medium, certain of the other nodes of the network or all of these other nodes of the network must relay this bandwidth distribution scheme. There is therefore a risk of overloading the bandwidth of the network or increasing the latency for setting up this distribution scheme.
There is therefore a need for a technique to reduce the latency for setting up, at each modification of the distribution of the bandwidth of the network (for example, in the case of the introduction of new nodes, the accommodation to new transmission conditions) of a new scheme for distributing radio data blocks in the overall bandwidth allocation scheme.